Search for rocket cob oven designs

Hello all!

First of all, thanks for this great place and all the usefull information shared!
Not long ago, I finished my first RMH, batchrocket 150mm with help from batchrocket.eu website and a question here and there on this forum. I'm very happy with the result, but still waiting to do the first real test on the cob to dry completely.

Now, having finished this project, we want to get into building an outdoor kitchen for the community. There's a little natural camping on our property this summer and for that and for us and for who ever passes by, we want to make a natural outdoor kitchen. Ofcourse, this kitchen needs to have a cob/pizza oven. I did a workshop where we built an oven like this but I'm not fully convinced of these smoke 'spitting' unefficient burning ovens while now knowing about rocket science and efficient burning.
I would like to combine the two techniques and make it into a very efficient/fast heating oven. Will also insulate good like with cob ovens. Researching about this combination, I don't find much usefull information or designs. I don't really like the idea of making the fire in the oven space, so hoped to make it below and maybe make a 125mm batchbox burn chamber and riser below leading into the oven (which would act as the bell).
I found a video from 'organic motion' on youtube where they do a similar design but with a J Tube.
Ideally you could light the rocket stove for a while and then when at temperature, close off the oxygen of the fire and cook with the heat that the cob absorbed.
To make sure it stays hot for long and no residues of the fire fall on top of our pizza's, i would probably need a lid to put on top of the whole where the riser is coming into the oven area (think to make that completely in the back of the oven)
I would also add a chimney on the side of the oven with opening as low as possible to make sure the cob  absorbs the heat as long as possible.
I'm sure i'm not the first one having this idea, knowing both rocket stoves and cob ovens are pretty popular.
Did somebody try something out already like this? Or has some proven designs? Etc?
I'm a bit insecure immediately making the oven that way as it's also for guestst to use etc.. but don't want to do 101 test builds maybe with some advise from you guys, I can manage this experimental build!
This is the video of the rocket cob oven I mean: https://youtu.be/DBK5K5HoKRw

Will try adding pics of my rmh build and outdoor kitchen plans.

Thanks ✌️

Hi Ruben;
Check out my outdoor kitchen build.  https://permies.com/t/164923/rocket-ovens/Build-Black-White-Rocket-Oven
A walker riserless core provides the heat.
The oven is brick, insulated with Morgan Superwool.
It can be run as a black or white oven.
My door is currently only 13" wide, it will be modified this summer to allow 16" pizza to slide in.

Thanks Thomas for your inspiration!
Although it's not really that kind of design i'm looking for..

Update on the progress.
We just started the outside kitchen today. We put the foundation, with root barrier, drainage pipe and old rubble that was still laying here from breaking out some old walls. We evened it out with some gravel and will start putting the stem wall with reused bricks from the property very soon. So that was my call to get into the details of the oven. Decided to make a batchrocket 125mm rmh system underneath the oven, letting the riser feed in the backside of the oven.
I'll make it a fully insulated cob oven with 10cm cob 10 insulation and 10 cob again. Inner diameter 80 cm.
Kind off like how the front of the firebox will look in the design I made. Very curious if I will get the efficiency I aim for here.
Current plans

Hi guys!
I've been too ambitious with timing and let go of the progress of the kitchen for a while as there were many other projects going on here.
After reflecting on the plans and getting all excited about rocket stoves again (as i'm using my batchrocket everyday now in winter) i want to get started with the oven to hopefully have a good functioning pizza/cob rocket oven during the coming warmer seasons.
Since i did some more research, I realised that that is the challenge with rocket cob ovens, having the base/ground of the oven warm enough to cook pizza's. And makes a lot of sense as heat rises and with fire underneath there's no fire laying on top of the floor like with usual cob ovens.
So I've been researching and found some interesting ideas/designs. My plan right now is to build a well insulated 150mm batchbox underneath and have the warm gases pass under the floor of the oven before
Entering the dome/bell. A bit like this design I stumbled upon.
https://lhalfo011.wixsite.com/rocket-vs-oven/my-design
My question here is how and out of what material to make this floor where the heat passes under. It has to be able to resist the chock temperatures from the rocket stove and hopefully store a good amount of heat for some time without became way too hot too quickly. I want to use as much local and local sourcable materials as possible so I was researching in casting something. Someone has advice on what to use to cast this floor so it will fit these requirements? Clay/cob would be easiest but will crack won't it? (I have it in the soil) My other idea is to use firebricks. But for that i'll have to create something where the firebricks are laying on and seal them with the fireproof mortar. Any suggestions on what to do?
For the chimney i'm not so sure yet either. Don't plan to make a double door like on the plan I linked. I'd like to go for most efficient use of the heat of course so having the chimney quite low in the oven or even having it in the area underneath the floor is my idea so far (although with this idea i wonder if the chimney would just pull the heat gases from the riser immediately before them entering the dome, that wouldn't be ideal ) any thoughts on that?  

I'm also wondering if adding a copper coil thermosyphon (around the riser or around the chimney or both) takes a lot of the efficiency of the oven part away. If not, I'll add something like this also so we'll have warm water for the dishes after.
Any thought/ideas or suggestions for this project?


Next to this oven i'd like to make a rocket cookstove as well. Will do some experimenting with j tube and an old cast iron cooktop soon.

Will add some pics of a quick sketch on my plan so far and the kitchen so far.

Enthousiastic rocket smile
Ruben

Any thoughts?

I built a rocket fired cob oven about 8 years ago, my first rocket and my first oven so experimenting. I did the traditional heavy mass all around, L-tube rocket beneath with multiple heat channels below the floor and multiple vents around the edges of the floor. A chimney at the front lets the exhaust escape.

I learned that this configuration does not want a thick floor; it bakes excellently but needs metal racks for the food so heat can circulate below. I think I would use firebrick for the floor again, but instead of bedding it in sand on a heavy brick base, I would make a carefully leveled set of brick ridges to support the ends of the floor bricks and let the heat channels directly meet most of the bottoms of the floor bricks. Firebrick transmits heat pretty fast, and I believe that would heat up quickly enough yet even out the heating.

The L-tube combustion core takes long sticks/logs and can be tuned to deliver the desired amount of heat.

Hi Glenn!

Thanks for your contribution to this topic man! This is exactly the type of 'experience' i'm looking for!
That's very valuable information! Amazing project and amazing lessons for the next builders! Thanks a lot!
So, if i understand correctly, in your design the floor is too thick to heaten up good to let's say pizza temperatures (250-300°c) ? And you suggest that having a single layer of fire bricks as the floor (where the hot gases touch the bottom of the fire bricks directly) would solve this problem?
That's amazing! That's exactly how I imagined to do it. In fact, i bought already fireproof tiles for it. They 20*20*3cm. Now i'm wondering, is that too thin? Maybe it'll get too hot? Other option would be firebricks 4cm thick. But they are quite a bit smaller so will make it harder to make a nice floor..
Any thoughts?

How about your chimney? Are you loosing a lot of heat through it as it is quite high in the 'bell'?
I'm considering using a bypass system, where the top one(that you can close) is at normal height to get the chimney pulling quickly, and the bottom one, under the floor/at the level of the floor.
Any thoughts?
Thanks man!

I think your large thin tiles would work excellently for the oven floor, as long as you add a diffuser below to spread out the direct flame from the heat riser. Something that makes the flames go in all directions under the floor, and able to circulate back under the middle between diffuser and floor, would most likely be ideal. Also, it would be better for the tiles to not have a single hot spot in the middle but be evenly exposed to heat.

My exhaust circulates around the oven space before going down a bit to enter the front chamber which opens to the chimney. The doorway between the chambers is sized according to traditional wood-fired oven door proportions and heights.

Hmm, yeah
Some kind off diffuser would be beneficial for sure..
I don't have a clue though what that diffuser could be made off..
My riser is entering the oven space completely at the back so actually it only has to push the heat forward and sideways..
I wonder if it's really necessary to have this as it will complicate the design quite a lot, I think.
Might not be too big of a problem if this hotter spot is completely at the back..
Do you see a sort off easy way to integrate a diffuser?
And how much space would this area unde the floor need? I have 7cm high fire bricks atm.. it might be a bit small, i think.. can get 11cm ones as well, or immediately 2 small ones on top of eachother..
Many possibilities..

Cob ovens are cool and I've been wanting one for myself for some time, as a functional show piece in my backyard.  But they are a pain to get to temperature. It takes so much time and wood. A twist on the rocket mass heater to create a 'rocket' wood oven that uses little wood and heats up faster than your conventional oven. I found this youtube giving a short explanation of how it works. Apparently heard that it can be adapted to be indoors as well... https://www.youtube.com/watch?v=kHjGQMoxFI4